This invention relates to a process for improving the flowability and preventing the agglomeration of finely ground dimerized 2,4-toluene diisocyanate by the addition of precipitated silicas and/or pyrogenic silicas having a hydrophobic surface.
At present, the only solid, relatively high melting diisocyanate that is available on the market is finely ground dimerized 2,4-toluene diisocyanate (trade product DESMODUR.RTM.TT of Bayer AG, West Germany) ##STR1## This material is used mainly in PVC primers and for the production of polyurethane rubber, where it is used for obtaining a homogeneous end product in a very fine form. A more recent field of application is use in polyurethane one-component systems based on solid polyisocyanates.
The commercial DESMODUR.RTM. TT product is in the form of a white powder having a particle size of from 2 to 25 .mu.m. In transport and storage, and particularly for applications in which the DESMODUR.RTM.TT powder must be dispersed in viscous liquids, the tendency of the fine solid particles to compact and agglomerate may cause difficulties.
The problem arose, therefore, of improving the flowability of the finely divided dimerized 2,4-toluene diisocyanate and reducing the tendency of the solid to agglomerate. This problem has been solved by adding certain types of silica to the polyisocyanate.